Analog optical communication links are known in the prior art. Conventional optical analog links employ intensity modulation techniques to convert the analog information into an optical signal. Analog optical links are utilized, for example, by the cable television industry to transmit video images using the conventional RF analog modulation format, as well as in numerous RF antenna applications.
In most optical analog links, the information is converted from RF (electrical) signals to optical signals through the use of an external Mach-Zehnder intensity modulator (MZI). Conventional electro-optic modulators (EOMs) are generally based on proton-exchanged or Ti-diffused waveguides in an optically active material, such as lithium niobate (LiNbO3). In operation, when an electric field is applied across an optically active waveguide, the optical path length of the waveguide will be altered, allowing the phase of the output signal to be controlled accordingly. This effect is used to both alter the phase of the light (i.e., phase modulators) and to produce amplitude modulation when the waveguide is placed within an interferometer.
LiNbO3-based devices are relatively large (having a length on the order of, for example, 75 mm), which makes them ill-suited for many current applications which require high density integration, as well as a high degree of linearity. Further, these devices are known to exhibit a “voltage sensitivity” (denoted as Vπ, which defines the amount of voltage required to provide a complete 180° phase shift) on the order of three volts. This relatively large Vπ has also been found to result in the following: (1) relatively low link gain, on the order of −26 dB at 10 mW input optical power; (2) a large noise factor (NF), on the order of 33 dB at 10 mW input optical power; and (3) large input third order intercept point (TOI) of greater than 19 dBm. Moreover, the power dissipation associated with conventional LiNbO3 modulators renders them essentially useless for applications where available power or power consumption is a concern.